Open circuit and ground detector for fire and burglar alarm system

ABSTRACT

The disclosed invention functions electronically to detect open circuits and grounds, and various combinations of same, on a four-wire circuit of the kind which includes two wires on the first side, two wires on the second, and a set of normally open contacts between the two sides. Each pair of wires is connected between base and emitter of a transistor and the contacts are disposed between the bights of the pairs of wires. The first and second transistors, connected in this manner, are employed to detect open circuits. Added to this combination are third and fourth transistors, utilized to detect grounds. These four transistors comprise branch paths which are connected to a common trouble-indicating circuit. The closing of the contacts causes to be nonconductive a fifth and sixth transistor, so that they trigger an alarm-indicating circuit.

United States Patent [191 Cook [ Nov. 5, 1974 1 OPEN CIRCUIT AND GROUND DETECTOR FOR FIRE AND BURGLAR ALARM SYSTEM [75] Inventor: Charles W. Cook, Huntsville, Ala. [73] Assignee: Avco Corporation, Huntsville, Ala.

[22] Filed: Apr. 30, 1973 [21] Appl. No.: 355,963

[52] US. Cl ..-340/409, 307/308, 340/255, 340/256, 340/276 [51] Int. Cl. G08b 19/00 [58] Field of Search 340/409, 276, 255, 256; 307/308 [56] References Cited UNITED STATES PATENTS 2,695,994 11/1954 Lode 340/409 3,210,751 10/1965 Shiraishi 340/256 3,252,156 5/1966 Muehter 340/276 Primary Examiner-David L. Trafton Attorney, Agent, or Firm-Char1es M. l-logan [57] ABSTRACT The disclosed invention functions electronically to detect open circuits and grounds, and various combinations of same, on a four-wire circuit of the kind which includes two wires on the first side, two wires on the second, and a set of normally open contacts between the two sides. Each pair of wires is connected between base and emitter of a transistor and the contacts are disposed between the bights of the pairs of wires. The first and second transistors, connected in this manner, are employed to detect open circuits. Added to this combination are third and fourth transistors, utilized to detect grounds. These four transistors comprise branch paths which are connected to a common trouble-indicating circuit. The closing of the contacts causes to be nonconductive a fifth and sixth transistor,

so that they trigger an alarm-indicating circuit.

5 Claims, 1 Drawing Figure AAA ItIlAAA VVIVV AAAAA OPEN CIRCUIT AND GROUND DETECTOR FOR FIRE AND BURGLAR ALARM SYSTEM BACKGROUND OF THE INVENTION The present invention pertains to burglar and fire detecting systems in which a plurality of transponders at customer locations are interrogated by a central station for the purpose of ascertaining the conditions of sensing equipment at the various customer locations.

The invention is of particular utility in a system of the type which comprises a first pair of transmission lines on a first side and a second pair on a second side, the pairs being inter-connected by the normally open contacts of a sensing device. That is to say, a sensing device, which detects the presence of a tire or trespasser, for example, responds to an alarm condition, by closing contacts 50. Intelligence is electrically transmitted from that device to the customers transponder over transmission lines such as those designated 11 and 12 for the first side and 13 and 14 for the second side.

The primary object of the invention is to maintain the intelligence-bearing capability and the functional integrity ofthese lines, notwithstanding the existence of various combinations of opens and grounds. For example, the preferred embodiment of the invention is required to operate with an open and/or ground on the first side and an open on the second side. Also with an open on the first side and an open and/r ground on the second side.

Another object of the invention is to detect and indicate the presence of a fault, either an open or ground, on any one of the four lines.

Another object of the invention is to provide an alarm and fault detector which operates in such a way that a trouble fault occurs and is indicated when any one of the four lines is open or grounded. An alarm condition causes an alarm indication whether or not a trouble fault exists.

BRIEF DESCRIPTION OF THE DRAWING For a better understanding ofthe invention, together with other objects, advantages and capabilities thereof,

reference is made to the following description of the' SPECIFIC DESCRIPTION OF THE INVENTION In order to assure that a fault will be indicated whenever any one of lines 11 or 12, on the first side, or lines 13 or 14, on the second side. becomes grounded, l provide a plurality of conductive paths into the base of a transistor 9 in a trouble-indicating network comprising transistors 9 and 21. More specifically, line I2, which is conductively related to line 11, is connected to the emitter of a transistor 15, via resistor 16. The base of that transistor is connected to the positive terminal 20 of a suitable bias source by resistor 17. The collector is connected via resistors 18 and 19 to the same terminal 20. The emitter of transistor is connected to ground via resistors 16 and 31. The bias connections are such that when either conductor 11 or 12 is grounded the emitter of. transistor 15 goes sufficiently negative that transistor 15 conducts and the collector tor 21 to conduct. The connections of transistor 22 comprising resistor 23, in series with its collector, resistors 24 and 32, in series with its emitter, and the series relationship between line 14 and resistor 24, are similar in that, when either line 13 or 14 is grounded, the emitter of transistor 22 goes negative relative to its'base and transistor 22 conducts, causing current flow through resistor 23, which causes the chain of transistors 9 and 21 to conduct.

Transistor 9 of the trouble indicating network is a PNP transistor with its emitter connected to terminal 20 and with resistor 19 connected between its base and emitter. The collector of transistor 9 works, via series resistor 25, shunt capacitor 26, and series resistor 27, into the base of NPN transistor 21, which has its emitter connected to the negative terminal 28 of the source of bias currents and which has a resistor 29 connected between its emitter and base. Whenever any one of lines 11, 12, 13, or 14 is grounded, so that one of transistors l5 and 22 conducts, then the transistors 9 and 21 conduct and a fault isindicated via the trouble line 30.

Since the emitter circuits of transistors 15 and 22 are returned to negative terminal 28 via resistors 31 and 32, respectively, a ground on any one of lines I1, 12,

' 13 or 14 will effectively short-circuit one of these two line 11 or 12 the base of transistor 34 goes positive relative to the emitter and transistor 34 conducts. Under an open-circuit condition the emitter is no longer directly conductively tied to the base. When transistor 34 conducts, transistor 9 and 21 conduct, indicating a fault. Transistors 34 and 35 have their collectors connected in series with the base of transistor 9, via resistors 36 and 37, respectively, and their bases are both connected to point 39 on a voltage divider comprising resistors l7 and 38. Lines 13 and 14 are connected between base and emitter of transistor 35. The operation of transistor 35 is similar to that of transistor 34 in the sense that an open circuit on line 13 or 14 causes transistors 35, 9 and 21 to become conductive, giving a signal on line 30.

The bases of transistors 34 and 35, respectively, are connected to the positive terminal 20 via resistors 43 and 44, the voltage at the base of transistor 34 being, in the preferred embodiment, twice that at the base of transistor 35.

The condition for giving an alarm signal is the rendering conductive of the alarm transistor 40 which is encircuited with fifth and sixth NPN transistors 41 and 42. The emitters of these two transistors are connected to terminal 20 by resistors 43 and 44, respectively. The base of transistor 42 is connected via resistor 45 to the emitter of transistor 34 and the base of transistor 41 is connected by resistor 46 to the emitter of transistor 35.

The positive terminal 20 is connected by resistor 47 and the separate branch resistors 48 and 49 to the collectors of transistors 41 and 42.

Transistor 41 conducts when either line 11 or 12 is grounded, this effect making the emitter negative going. Similarly transistor 42 conducts when there is a ground on either line 13 or 14. The condition for conductivity of the alarm transistor 40 is that neither transistor 41 nor 42 conducts. This condition is achieved when the contacts 50, normally open, close, because that action makes the base of41 have the same potential as its emitter and the base of 42 have the same po tential as its emitter, so that neither transistor 41 nor 42 conducts. Both of these transistors must be off in order to sound the alarm. The collectors of both are in circuit with the base of the alarm transistor 40 which has an output line 51 and a resistor 47 between its emitter and base. lts emitter is connected to terminal 20.

All of the transistors are of the NPN type with the exception of transistors 9 and 40, which are PNP. 1n the preferred form of circuit the value of resistor 31 istwice that of resistor 43. The value of resistor 32 is equal to that of resistor 43 and is half that of resistor 31. The voltage at the base of transistor 34 is two-thirds of that at terminal 20. The voltage at the base of transistor 35 is one-third of that at terminal 20. The value of resistor 44 is twice that of either of resistors 32 and 43. The illustrative parameters and values herein mentioned are not limiting. In the preferred embodiment transistor 42 is so biased as to conduct in the absence of any fault or alarm. In the preferred embodiment the voltage at A is sufficiently greater than that at B to assure turn-off of transistor 42 when contacts 50 are closed.

The following parameters have been found suitable in one working embodiment of the invention:

Resistor I7 6800 ohms Resistor 38 2200 ohms Resistor l8 10,000 ohms Resistor l6 I000 ohms Resistor 23 10.000 ohms Resistor 24 [000 ohms Resistor 3o l0,000 ohms Resistor 37 l5,000 ohms Resistor 3l 6800 ohms Resistor 32 3300 ohms Resistor 29 l00,000 ohms Resistor 27 22.000 ohms Resistor 45 I0,000 ohms Resistor 4h 10.000 ohms Resistor 25 100.000 ohms Resistor 414 10,000 ohms Resistor 4) 15.000 ohms Resistor 47 l00,000 ohms Resistor 43 3300 ohms Resistor 44 6800 ohms Resistor l) 000 ohms Capacitor In I mierolttrad Voltage at Terminal I2 volts The invention comprises. in a burglar and fire alarm system of the type which includes a sensor having a normally open pair of contacts 50, a first pair of transmission lines 11, 12 connected to one of said contacts and a second pair of transmission lines 13, 14 connected to the other end of said contacts, the combination of:

a first transistor 34 having an emitter and a base and a collector,

a second transistor 35 having an emitter and a base and a collector,

said contacts being connected between the bights of the pairs of transmission lines,

the first and second lines 11, 12 being connected between the base and emitter of the first transistor and the third and fourth lines being connected between the base and emitter of the second transistor,

a trouble indicating network which responds to collector flow in either the first or second transistor, the collectors of the first and second transistors being in series with said network,

and means 36, 43, 37, 44 for so biasing the first and second transistors that if an open circuit develops in any of said lines, permitting the base of one of said first and second transistors to become disconnected from its emitter, then collector current of one of the first and second transistors flows into said trouble-indicating network.

The invention also comprises third and fourth transistors 15 and 22 each having a collector and a base and an emitter,

and means 16, 18, 23, 24, 31, 32 for biasing said third and fourth transistors so that a ground on any of the lines causes the emitter of one of the third and fourth transistors to become biased in a conductive direction and to apply collector current to said trouble-indicating network.

The invention further comprises an alarm indicating network 40 and fifth and sixth transistors 41, 42 each having a base and an emitter and a collector, the emitters of the fifth and sixth transistors being respectively coupled to the bases of the first and second transistors 34, 35, and the bases of the fifth and sixth transistors being coupled to the emitters of the second and first transistors,

means 47, 48, 49 for completing the biasing of said fifth and sixth transistors so that both are nonconductive when said contacts are closed and so that the sixth transistor is conductive in the absence of any ground or open circuit on said lines,

the alarm network being in series with the collectors of the fifth and sixth transistors and responding to a nonconducting condition of both the fifth and sixth transistors to send out an alarm.

While there has been shown and described what is at present believed to be the preferred embodiment of the invention, it will be understood by those skilled in the art that various changes and modifications may be made therein without departing from the scope of the invention as defined in the appended claims.

Having described my invention, 1 claim:

1. The combination of first and second transistors each having a base and an emitter and a collector,

a source of bias currents,

third and fourth transistors each having a base and an emitter and a collector,

a first conductive path between the base and emitter of the first transistor,

a second conductive path between the base and emitter of the second transistor,

the collector-emitter circuits of the four transistors being connectedin parallel, and

means, including a first resistor between ground and the emitters of the first and third transistors and a second resistor between ground and the emitters of the second and fourth transistors, for biasing the four transistors so that, in response to an open on either of said conductive paths one of the first and second transistors becomes conductive and so that in response to a ground on either of said paths one of said resistors is short-circuited and one of the third and fourth transistors becomes conductive,

lectors of the fifth and sixth transistors being connected in parallel,

an alarm indicator in series with the collectors of said fifth and sixth transistors and responsive to the ab- 3 trouble-indicating network Coupled t the eoheesence of collector currents in both of the fifth and tors of all of said transistors and responsive to coli th transistors t id an alarm, d teetet ehtteht th of the first, Second, third of means for completing the biasing of said fifth and fourth transistors to indicate a fault in one of said i th transistors so h h i h transistor Conductive P ducts in the absence of any open or ground in einormally open switch contacts between said conduc- 0 h h tive paths, 5. ln a burglar and fire alarm system of the type htth ahdvstxth ttahststets each havlhg 11 base and which includes a sensor having a normally open pair of ethtttet t a eeheetet the emitters of the htth and contacts, a first pair of transmission lines connected to StXth ttahststets hethg eehheeted t0 t bases of the one of said contacts and a second pair of transmission htst t Seeehd ttahslstetst 'P h y the bases 15 lines connected to the other one of said contacts, the of the fifth and sixth transistors being coupled to combination f: the etmtters of the second and first ttahststotsz a first transistor having an emitter and a base and a spect vely, and the collectors of the fifth and sixth Collector, trahststhrshemgFohhhctett m parallel a second transistor having an emitter and a base and an alarm indicator in series with the collectors of said a collector fifthand sixth transistors and responsive to the abthe first and Second lines being Connected in Series S.enCe of chllector currehts m both of the fifth and between the emitter and base of the first transistor Smh translstors 9 f alarm *h and the third and fourth lines being connected in means for Completmg the bmsmg on 531d fifth and series between the emitter and base of the second sixth transistors so that the sixth transistorcontransistor, ducts m the absence of any Open or ground m a trouble-indicating network which responds to colthet path I lector flow in either the first or second transistor, The.combtnauon of first. Second trmslstors the collectors of the first and second transistors each having a base and an emitter and a collector, being in Series with Said network fz g of i th b t th means for biasing said first and second transistors so rs an secon con uc 1V6 pa 5 e we e that an open on any of the lines causes the emitter sped-we bases and emitters of the first and Second of one of the first and second transistors to become transistors biased in a conductive direction and to apply colthird and fourth transistors each having a base and an I I emitter and a Collector ector current to said trouble-indicating network, the collector-emitter circuits of said four transistors gg g g gi gg gg gzggs havmg a collector bitween ground and conhctorf of h third t transistors being the emitters of the first and third transistors and a m Senes h troublei'mdlcatmg network, second resistor between ground and the emitters of 40 means for so blasmg the h and h h trahslstors the second and fourth transistors, for biasing said that ground develops any of Stud lmes h four transistors so that, in response to an open cirtot eutteht t r1 Of the th rd and fourth transistors cuit on any of said conductive paths one of the first hows h atd ttouhtethdtcahhg network, and second transistors becomes conductive and so ah atarth thdtchtthghetwotk that in response to a ground on any one of Said fifth and sixth transistors each having a baseand an paths one of said resistors is short-circuited and ethtttet t a collector the ehhttets of the htth and one of the third and fourth transistors becomes Stxth ttahststots bethg respeettvety e p t0 the Conductive. bases of the first and second transistors, and the 3. The combination in accordance with claim 2, and bases of the t ahd Sixth transistors bethg ha trouble-indicating network coupled to the collectors P t0 the emtttets of the Seeohd and first transisofall of said transistors and responsive to collector curtors, and rent in any of them to indicate a fault in one of said means for eomptetthg the btasthg of Seth htth ahd Conductive paths srxth transistors so that both are nonconductive 4 The combination in accordance with claim 3, when COfltZlQlIS 3.1'6 ClOSed and SO that the SiXth normally open contacts between said conductive transistor is conductive when said contacts are paths, open and in the absence of any ground or open cirfifth and sixth transistors each having a base and an cuit on said lines,

emitter and a collector, the emitters being 0011- the alarm-indicating network being in series with the nected to the bases of the first and second transiscollectors of the fifth and sixth transistors and retors, respectively, the bases of the fifth and sixth 0 sponding to a nonconducting condition of both the fifth and sixth transistors to send out an alarm.

transistor being coupled to the emitters of the second and first transistors, respectively, and the col- 

1. The combination of first and second transistors each having a base and an emitter and a collector, a source of bias currents, third and fourth transistors each having a base and an emitter and a collector, a first conductive path between the base and emitter of the first transistor, a second conductive path between the base and emitter of the second transistor, the collector-emitter circuits of the four transistors being connected in parallel, and means, including a first resistor between ground and the emitters of the first and third transistors and a second resistor between ground and the emitters of the second and fourth transistors, for biasing the four transistors so that, in response to an open on either of said conductive paths one of the first and second transistors becomes conductive and so that in response to a ground on either of said paths one of said resistors is short-circuited and one of the third and fourth transistors becomes conductive, a trouble-indicating network coupled to the collectors of all of said transistors and responsive to collector current in any of the first, second, third or fourth transistors to indicate a fault in one of said conductive paths, normally open switch contacts between said conductive paths, fifth and sixth transistors each having a base and an emitter and a collector, the emitters of the fifth and sixth transistors being connected to the bases of the first and second transistors, respectively, the bases of the fifth and sixth transistors being coupled to the emitters of the second and first transistors, respectively, and the collectors of the fifth and sixth transistors being connected in parallel, an alarm indicator in series with the collectors of said fifth and sixth transistors and responsive to the absence of collector currents in both of the fifth and sixth transistors to provide an alarm, and means for completing the biasing on said fifth and sixth transistors so that the sixth transistor conducts in the absence of any open or ground in either path.
 2. The combination of first and second transistors each having a base and an emitter and a collector, a source of bias currents, first and second conductive paths between the respective bases and emitters of the first and second transistors, third and fourth transistors each having a base and an emitter and a collector, the collector-emitter circuits of said four transistors being connected in parallel, and means, including a first resistor between gRound and the emitters of the first and third transistors and a second resistor between ground and the emitters of the second and fourth transistors, for biasing said four transistors so that, in response to an open circuit on any of said conductive paths one of the first and second transistors becomes conductive and so that in response to a ground on any one of said paths one of said resistors is short-circuited and one of the third and fourth transistors becomes conductive.
 3. The combination in accordance with claim 2, and a trouble-indicating network coupled to the collectors of all of said transistors and responsive to collector current in any of them to indicate a fault in one of said conductive paths.
 4. The combination in accordance with claim 3, normally open contacts between said conductive paths, fifth and sixth transistors each having a base and an emitter and a collector, the emitters being connected to the bases of the first and second transistors, respectively, the bases of the fifth and sixth transistor being coupled to the emitters of the second and first transistors, respectively, and the collectors of the fifth and sixth transistors being connected in parallel, an alarm indicator in series with the collectors of said fifth and sixth transistors and responsive to the absence of collector currents in both of the fifth and sixth transistors to provide an alarm, and means for completing the biasing of said fifth and sixth transistors so that the sixth transistor conducts in the absence of any open or ground in either path.
 5. In a burglar and fire alarm system of the type which includes a sensor having a normally open pair of contacts, a first pair of transmission lines connected to one of said contacts and a second pair of transmission lines connected to the other one of said contacts, the combination of: a first transistor having an emitter and a base and a collector, a second transistor having an emitter and a base and a collector, the first and second lines being connected in series between the emitter and base of the first transistor and the third and fourth lines being connected in series between the emitter and base of the second transistor, a trouble-indicating network which responds to collector flow in either the first or second transistor, the collectors of the first and second transistors being in series with said network, means for biasing said first and second transistors so that an open on any of the lines causes the emitter of one of the first and second transistors to become biased in a conductive direction and to apply collector current to said trouble-indicating network, third and fourth transistors each having a collector and a base and an emitter, the collectors of the third and fourth transistors being in series with said trouble-indicating network, means for so biasing the third and fourth transistors that if a ground develops in any of said lines, collector current of one of the third and fourth transistors flows into said trouble-indicating network, an alarm indicating network, fifth and sixth transistors each having a base and an emitter and a collector, the emitters of the fifth and sixth transistors being respectively coupled to the bases of the first and second transistors, and the bases of the fifth and sixth transistors being coupled to the emitters of the second and first transistors, and means for completing the biasing of said fifth and sixth transistors so that both are nonconductive when said contacts are closed and so that the sixth transistor is conductive when said contacts are open and in the absence of any ground or open circuit on said lines, the alarm-indicating network being in series with the collectors of the fifth and sixth transistors and responding to a nonconducting condition of both the fifth and sixth transistors to send out an alarm. 